Shelf unit



FIG. 1 is a perspective view of a shelf unit showing my design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a right view thereof;

FIG. 5 is a left view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken line showing is included for the purpose of illustrating environmental structure and forms no part of the claimed design. 

CLAIM The ornamental design for a shelf unit, as shown and described. 